The present invention relates to a illumination type push button switch used in an electronic apparatus, such as a portable telephone or a personal computer.
Recently, electronic apparatuses including a portable telephone and a personal computer have better functions and cover a broader spectrum. Push button switches used in an operating part of the apparatuses are required to light a push button for illuminating to enable an operation even in dark.
The conventional illumination type push button switch will be described with reference to FIG. 5.
FIG. 5 is a sectional view of the conventional illumination type push button switch. Dark-colored push button 1 made of insulating resin includes, at its top surface, display part 1A which is, for example, semitransparent or milk-white and is exposed in the form of a letter, a mark, a design or the like. Switch contact 2 disposed below button 1 includes wiring board 3, flexible insulating film 4, insulating spacers 5 each having both surfaces coated with adhesive for bonding wiring board 3 and insulating film 4 together, plural fixed contacts 3A on a top surface of wiring board 3, and plural movable contacts 4A on a bottom surface of insulating film 4. Fixed and movable contacts 3A and 4A face each other at a predetermined space. Switch contact 2 thus functions as a membrane switch. Light-emitting diode (LED) 6 is mounted on the top surface of wiring board 3 near fixed contact 3A. Insulating film 4 and insulating spacer 5 have respective holes through which LED 6 is inserted. Board 7 is mounted on a bottom surface of wiring board 3. Case 8 made of insulating resin covers these elements and has, at its top side, a hole through which button 1 projects vertically movably. The illumination type push button switch is thus configured.
When specified push button 1 is pressed downward, insulating film 4 is pressed by push part 1B and sags, thereby allowing corresponding movable contact 4A on the bottom surface of this film 4 to contact with corresponding fixed contact 3A on the top surface of wiring board 3. This action allows switch contact 2 to establish electrical connection and disconnection.
When LED 6 on the top surface of wiring board 3 emits light, display part 1A of push button 1 over LED 6 illuminates from behind with the light, which thus facilitates the identification of button 1 even in dark.
In the conventional push button switch described above, since LED 6 has light emission directivity, the light emitted by LED 6 lights display part 1A of push button 1 weak if display part 1A is in a position out of alignment with LED 6. Further, if many push buttons 1 are arranged, the number of LEDs 6 must be equal to the number of buttons 1. This increases the number of components, and further, it takes time, for example, to make the holes in insulating film 4 and insulating spacers 5 and to mount LEDs 6 to wiring board 3. This makes the conventional push button switch expensive accordingly.
A push button switch includes a push button, a switch contact for establishing electrical connection and disconnection when the push button is pressed and released, a board mounted to the switch contact to face the push button across the switching contact, and an EL element mounted to a substrate to face the switch contact across the substrate. The board has a through-hole formed therein near the switch contact. The EL element includes a light-emitting part including a light-transmitting electrode layer, a luminescent layer, and a back electrode layer overlaid.